New York has finally figured out where the deadly Legionnaires' disease bacteria started

The location of the source of the Legionnaires' disease outbreak. Lucas Jackson NEW YORK (AP) — A historic hotel's rooftop air-conditioning unit is the source of a Legionnaires' disease outbreak that has killed 12 people and sickened more than 100 in the Bronx, city Health Commissioner Mary Bassett said Thursday.

After extensive sampling and testing of Legionnaires'-causing bacteria, laboratories have matched the strain found in the hotel's rooftop unit — also called a cooling tower — with the strain found in 25 patients, some of whom died, Bassett said.

"The outbreak is over," Bassett said, noting the maximum incubation period has passed since the last new report of someone coming down with symptoms.

Dr. Jay K. Varma, a deputy health commissioner for disease control, said health officials investigating the outbreak learned nine days into their probe, on July 29, that a guest who had stayed at the hotel had become ill.

In all, there have been 128 cases and almost all patients hospitalized with the disease have been discharged, officials said. But it's unclear whether every patient walked right by the hotel; mist can travel up to a mile, under some conditions, officials said.

The outbreak has become the city's most significant public health crisis since last fall's Ebola scare. For more than a month, cases of Legionnaires' — a form of pneumonia especially dangerous for the elderly and for people with underlying health issues — have been reported throughout a section of the South Bronx, the city's poorest neighborhood.

Cooling towers in 18 buildings tested positive for the bacteria, and the outbreak prompted city and state officials to require the testing and inspection of building cooling towers across the state. The towers emanate warm mist that can spread bacteria.

The Opera House Hotel's building is more than a century old and once housed performances by Harry Houdini, the Marx Brothers and George Burns. It's in the heart of the South Bronx.

After speculation last week on the source of the outbreak, the hotel said that its 2-year-old cooling tower has been cleaned routinely and that managers acted quickly to get it cleaned again after learning of the Legionnaires' problem.

Glenn Isaacs, vice president of owner Empire Hotel Group, at the time defended its quick response to the outbreak and even complained that city health officials hadn't been forthcoming. City officials have said they gave hotel personnel all the information they could.

But on Thursday, the hotel, which was open, issued a statement saying that city and state health officials "have kept us fully informed" and pointed out that a test Wednesday was negative for the Legionnaires'-causing bacteria.

"Given the recent events, we have decided to be especially cautious going forward," the hotel said.